Herpes simplex virus type 1 (HSV-1) is the leading cause of infectious corneal blindness and viral induced encephalitis. HSV induced encephalitis (HSE) leads to a significant number of new cases each year, including 2,000 new cases each year in the United States. Recurrent eye disease and HSE can be induced long after the initial infection because HSV-1 has the potential to establish latency in sensory neurons, and then reactivate from latency. In spite of extensive viral gene expression during acute infection of sensory neurons, many neurons survive and establish latency. External stimuli can induce reactivation from latency resulting in virus shedding, recurrent disease, and spread to uninfected individuals. The only abundant viral RNA expressed during latency is the latency-associated transcript (LAT). LAT inhibits apoptosis in trigeminal ganglia of infected rabbits or cultured cells. The LAT sequences that inhibit apoptosis are also necessary for reactivation from latency. Recent studies demonstrate that an antibody directed against a novel open reading frame located within the first 1.5 Kb of LAT coding sequences recognizes a protein in human neuroblastoma cells or trigeminal ganglia of mice infected with a LAT expressing HSV-1 strain, but not a LAT null mutant. Additional studies presented in this application demonstrate that mutating the start codons in the first 1.5 Kb of LAT coding sequences reduces the ability of this fragment to inhibit apoptosis in cultured neuroblastoma cells. The project investigators hypothesize that expression of LAT encoded proteins plays a role in the latency-reactivation cycle. The long-term goals of the project investigators are to identify virus and host factors that regulate latency. The Specific Aims of this application are the next step in reaching our long-term goals. Studies in Specific Aim 1 will test whether LAT protein coding sequences within the 1.5 Kb LAT fragment are expressed in trigeminal ganglia of infected mice. Studies in Specific Aim 2 will test whether a LAT encoded protein inhibits apoptosis. Studies in Specific Aim 3 will develop recombinant viruses that will not be able to express LAT proteins. The research planned is innovative because it will test whether a protein encoded by LAT plays a role in the latency-reactivation cycle. Completion of these studies will enhance our understanding of how LAT regulates the HSV-1 latency-reactivation cycle. This application will develop antiserum that will recognize proteins encoded by the HSV-1 LAT. Studies will also determine whether LAT encoded proteins inhibit apoptosis, and whether these proteins are necessary for the latency reactivation cycle. [unreadable] [unreadable] [unreadable]